Successful management of tumors in the brain, head and neck is limited by potential damage to normal brain tissue caused by ionizing radiation. Although early symptoms are treatable, the delayed onset of cognitive and motor dysfunction s irreversible and contributes to morbidity and mortality. Neuroinflammatory changes, including activation of glial cells and expression of cytokines and other proinflammatory mediators, are a consistent feature of brain irradiation injury. Moreover, successful administration of corticosteroids for treatment of acute and chronic symptoms implicates the importance of inflammation-related events in radiation-induced injury and/or vulnerability. Based on their key roles in neuroinflammation and brain injury, and preliminary studies detailed in this proposal, we hypothesize that IL-1b and COX-2 are critical mediators of brain inflammation following radiation exposure. Studies in numerous systems, including our own investigations in whole brain, place COX-2, working through production of PGE2, as a downstream mediator of IL-1b action. Together, these findings suggest the hypothesis that neuroinflammation following radiation injury is dependent on an IL-1b/COX-2 pathway. Moreover, interference with this path may confer protection to normal tissue radiation injury. Three specific aims are proposed to establish the roles of IL-1 and COX in early and late brain tissue reaction following radiation exposure. Aim 1 utilizes 3 lines of knockout mice with defective IL-1 signaling pathways (null for IL-1R1, IL-1a, and IL-1b). Aim 2 will confirm the role of IL-1 by investigating brain irradiation responses in somatic mosaic mice engineered to regionally overexpress IL-1b or IL-1Ra. The final aim utilizes pharmacological and gene deletion approaches to investigate the specific role of COX-2 in CNS radiation responses. This work will provide a better understanding of the molecular and cellular mechanisms contributing to early and delayed effects, and may directly implicate specific targets for prevention and treatment of brain radiation injury.